For example, in a machine tool, a full closed loop position control device is used for positioning a table or the like to be driven with high accuracy. As described in Patent document 1, the full closed loop position control device includes a first position detector for detecting a rotation position of a motor and a second position detector for directly detecting a position of a drive object driven by the motor. The full closed loop position control device controls a position of a drive object based on an inputted position command value, a rotation position of the motor which is detected by the first position detector, and the position of the drive object which is detected by the second position detector.
On the other hand, in a machining line used in a mass-production, stopping of machine working causes stopping of the whole line. Moreover, sudden stop becomes a problem causing a delay in a delivery time of parts. Therefore, if abnormality or duration of life of each unit of a machine tool can be detected in advance, it is possible to take countermeasure such as replacing the part while a line is not in operation. Thus, a diagnostic function of a damage state is desired in a machine tool. A conventional full closed loop position control machine does not have a function for diagnosing a damage state of a drive object although the positioning accuracy is intended to be improved.
For example, as described in Patent document 2, diagnosing an abnormality detection of a feed spindle can be conducted by attaching a function for determining whether a motor torque exceeds a set threshold value.    Patent document 1: Japanese Unexamined Patent Publication No. 2002-157018    Patent document 2: Japanese Unexamined Patent Publication No. 2000-237908